A few rules for what constitutes an "indie bundle":
1. Typically, one of those thingies where you pay whatever you want for like, a dozen games or whatever.
2. Proceeds must go to charity or directly to the devs; none of that "EA Indie Bundle - $40 for two Shank games and Peggle!" crap.
3. Cannot be sold through Steam or GOG - if you've bought an indie bundles, I think you know what I'm getting at, basically.
I know this one might be hard, since even I confess that I only get them because they're cheap and 80% of the games in them don't interest me (I give the rest away to you guys! :D). But for me, it's easily Jamestown, by a pretty fair margin. To sum it up, it's a top-down Shmup, similar to Raiden, Thunderforce, Giga Wing or Ikaruga. However, it takes a lot of the tropes of these game and throws them out the window; there are no power-ups - you choose from one of four pre-built ships, each with unique powers. Instead, you have this system called "vaunt", where you release a bullet-absorbing shield and get powered-up weapons. The more bullets you absorb and enemies you kill during vaunt, the more points you accumulate. It graphics are 16-bit looking without being pretentious. A lot of indie games are all, "LOOK GUYS, LOOK HOW HIP WE ARE, 8-BIT GRAPHIX!!!!!1"... This one actually looks really good. The sprite art is amazing, and the music is absolutely fantastic - probably one of the 50 best OSTs I've heard heard, I'm serious!
But yeah. What great games have YOU discovered without breaking the bank?